1. Field of the Invention
The present invention relates to transmissions of the toroidal race rolling traction type. It relates in particular to ratio varying components (“variators”) for such transmissions, in which each of a set of rollers transmitting traction between an input disc and an output disc is connected to a hydraulic mechanism by which it is positioned, the roller position being a key factor in determining the transmitted ratio.
2. Background Art
Variators of this type are well known in the art, for example from GB-C-1395391, GB-A-2107009, EP-A-0078125 and EP-A-0133330. In common with most prior art variators, these specifications show a set of three rollers transmitting traction between a rotatable input disc and a coaxial and contra rotating output disc, each roller being spaced from the others by 120° of arc around the common axis of the discs. The ratio transmitted from the input to the output disc by each roller is caused to vary by changing the position of that roller in a direction substantially tangential relative to the centre circle of the common torus presented by the input and output disc races. The mechanism for imparting that tangential movement to at least some of the rollers comprises pistons formed at opposite ends of the roller carriage, that is to say the structure carrying the bearings on which the roller rotates, and movable within hydraulic cylinders.
In the prior art arrangements, the piston and cylinder assemblies for controlling the rollers necessarily project from the casings of the variator. Whilst this does not cause a problem from an operational point of view, it can be detrimental if the available space for installing the variator is limited.
EP-A-0538357 addresses this problem by positioning the cylinders to lie to the same side of a common plane including the axis of the discs. This improves the situation considerably but still results in lateral projections for the piston/cylinder arrangements.